1. Field of the Invention
The present invention relates to the control of the amount of residual solvent in proteinaceous materials and in particular to the control of the amount of residual solvent in comminuted proteinaceous materials that have been admixed with hydrocarbon solvent in a process for the separation of oil therefrom and/or in a process for the separation of fractions differing in protein content.
As used herein, proteinaceous material consists of soya beans and rapeseed. The outer coat of the proteinaceous material, which is also known as bran or the seed coat, may have endosperm attached thereto. The expression "gum" used herein refers in particular to water-soluble gums, if present in the particular proteinaceous material.
The proteinaceous materials are a potential source of a wide variety of useful products. Examples of such products are flour, starch, protein-enriched and protein-depleted products, bran, gum and oil, depending on the particular proteinaceous material. Traditional techniques used in the food processing industry, if available, for the treatment of proteinaceous material so as to effect the separation of the proteinaceous material into fractions of differing composition are capable of improvement, for example, with respect to energy requirements, potential pollution problems and the taste and/or color of products. In other instances, techniques may not be available for the conversion of the proteinaceous material into commercially viable products, for example, products of increased protein content.
2. Description of the Prior Art
Processes for the separation of proteinaceous material into fractions, especially proteinaceous fractions, in which the comminuted proteinaceous material or fractions thereof are admixed with hydrocarbon solvents for any oil in the material, are known. Such processes are disclosed by R. W. Oughton in U.S. Pat. Nos. 4,154,728, issued May 15, 1979, and 4,208,260, issued June 17, 1980.
The use of hydrocarbon solvents, especially hexane, in order to de-oil proteinaceous materials containing oil, e.g., soya beans and cottonseed, is known. Moreover, in some countries the amount of residual solvent in the de-oiled material, i.e., the amount of solvent remaining in the de-oiled material after separation from the oil bearing miscella, is subject to government regulation. For instance, under U.S. Food and Drug Administration Regulation No. 172,894, the amount of residual hexane in cottonseed meant for human use must be less than 60 ppm.
Several methods are known for reducing the amount of residual solvent in products that have been in contact with hydrocarbon solvents. For example, de-oiled soya beans have been treated with vacuum or steam or have been heated in ovens to promote evaporation of residual solvent. However, it has been found that even with intensive application of such methods, it is difficult to obtain products containing less than 60 ppm of residual solvent. Moreover, prolonged heating of proteinaceous products tends to result in denaturing of the protein.
A process for reducing the amount of residual solvent in soya beans is disclosed by W. G. Shultz in U.S. Pat. No. 3,966,981, which issued June 29, 1976. In that process, soya beans that contain residual hexane as a result of a de-oiling step, are extracted with liquid carbon dioxide under conditions whereby the carbon dioxide remains in a liquid state. A process for the removal of residual solvent from proteinaceous material, especially isopropanol from fish protein, by treating with air having a temperature of 40.degree.-90.degree. C. and at least 50% relative humidity, is disclosed in Canadian Pat. No. 1,052,170 of T. Knutsen et al., which issued Apr. 10, 1979.
In spite of the methods known in the art, there is a need for an improved process for controlling the amount of residual solvent to a level of less than 60 ppm in products that have been in contact with hydrocarbon solvents.